PET/Bone Scan Response as a Prognostic Indicator Following Spine Stereotactic Body Radiotherapy

Summary: Magnetic Resonance Imaging (MRI) is widely used for diagnosing and monitoring spinal metastases. However, its interpretation can be challenging due to influences such as osteoradionecrosis, fibrosis, or other non-tumor-related conditions. Nuclear imaging techniques, including PET scans and bone scans, can complement MRI in evaluating treatment response. This study presents nuclear response following spine stereotactic body radiotherapy (SBRT), integrated with other imaging modalities for comprehensive assessment. We conducted a retrospective analysis of patients with spine metastases treated with SBRT between 2014 and 2020. Patients who underwent PET or bone scans before and after radiation were included. Scan activity changes were categorized into complete response, stable disease, partial response, or disease progression. Contrast-enhanced MRIs were obtained before and after SBRT. We also examined factors such as age, sex, concurrent systemic therapy (administered within 4 weeks of radiation), radiotherapy fractionation, treatment volume, pathology (radiosensitive vs. radioresistant), and systemic disease status (stable vs. progressive). Kaplan-Meier and cox regression were used to outcomes. 47 patients with a median follow-up of 43.4 months. The median SBRT dose was 27 Gy, with a median BED10 of 51.3 Gy. Partial vertebra coverage was seen in 74% of cases, and 89% received multi-fraction treatment. Single spinal levels were treated in 62% of patients. Histologically, the cohort included breast cancer (21%), non-small cell lung cancer (15%), sarcoma (12%), and prostate cancer (12%). Systemic disease was stable in 57% of patients, while 43% had disease progression. PET scans were performed in 62% of patients, and bone scans in 38%. FDG-F18 PET scan done in 86% of them, Gallium 68 dotatate in 10% and F18FACBC in 4%. Based on nuclear studies, a complete response was observed in 72% of patients, a partial response in 12%, stable disease in 7%, and disease progression in 9%. The median time to complete metabolic response was 13 months (range 0.4-122 months). In the univariate analysis, systemic disease status (HR 5.85, 95% CI 1.18-28.92, p = .03) and nuclear complete response (HR 3.63, 95% CI 1.81-7.29, p < .001) were significantly associated with local control. In the multivariable analysis, nuclear complete response remained significant (HR 3.22, 95% CI 1.49-6.97, p = .003), while systemic disease status was not (HR 2.14, 95% CI 2.15-15.65, p = .45). Other variables, such as age, sex, concurrent systemic therapy, prescribed dose, fractionation, PTV, and pathology, were not significantly associated with outcomes in either analysis. The 2-year LC was 91% and OS was 63%. Spine SBRT continues to demonstrate a high rate of local control. PET or bone scan responses were linked to sustained disease control, with 91% of cases showing complete, partial, or stable disease. A nuclear complete response was associated with durable disease control in follow-up scans. Khaled Dibs (he/him/his), MD (Presenting Author) - The Ohio State University; Joshua D.. Palmer, MD (Co-Author) - Department of Radiation Oncology, The James Cancer Hospital and Solove Research Institute at The Ohio State University Wexner Medical Center; Evan Thomas (he/him/his), MD, PhD (Co-Author) - The Ohio State University; Raju Raval (he/him/his), MD, DPhil (Co-Author) - The Ohio State University; Sasha Beyer (she/her/hers), MD, PhD (Co-Author) - The Ohio State University; Vikram Chakravarthy, MD (Co-Author) - The Ohio State University; Brad Elder (he/him/his), MD (Co-Author) - The Ohio State University; Eric Bourekas, MD (Co-Author) - The Ohio State University; Daniel Boulter (he/him/his), MD (Co-Author) - The Ohio State University; Ahmed Elguindy (he/him/his), MD (Co-Author) - The Ohio State University; Eugene Yap (he/him/his), MD (Co-Author) - The Ohio State University; Emile Gogineni (he/him/his), DO (Co-Author) - The Ohio State University; Russell Lonser (he/him/his), MD (Co-Author) - The Ohio State University; Arnab Chakravarti (he/him/his), MD (Co-Author) - The Ohio State University; Dukagjin Blakaj (he/him/his), MD, PhD (Co-Author) - The Ohio State University